New cell line. Epithelial cell line and subline established from premalignant mouse mammary tissue

Single-cell analysis reveals Comma-1D as a unique cell model for mammary gland development and breast cancer

The mammary epithelial tree contains two distinct populations, luminal and basal. The investigation of how this heterogeneity is developed and how it influences tumorigenesis has been hampered by the need to perform these studies using animal models. Comma-1D is an immortalized mouse mammary epithelial cell line that has unique morphogenetic properties. By performing single-cell RNA-seq studies we found that Comma-1D cultures consist of two main populations with luminal and basal features and a smaller population with mixed lineage and bipotent characteristics. We demonstrated that multiple transcription factors associated with the differentiation of the mammary epithelium in vivo also modulate this process in Comma-1D cultures. Additionally, we found that only cells with luminal features were able to acquire transformed characteristics after an oncogenic HER2 mutant was introduced in their genomes. Overall, our studies characterize at a single-cell level the heterogeneity of the Comma-1D cell line and illustrate how Comma-1D cells can be used as an experimental model to study both the differentiation and the transformation processes in vitro.

Role of Rac1/WAVE2 Signaling in Mediating the Inhibitory Effects of γ-Tocotrienol on Mammary Cancer Cell Migration and Invasion

The majority of breast cancer deaths result from the progression of this disease to a metastatic phenotype. Rac1 and Cdc42 are Rho family members that together with their downstream effectors, Wiskott-Aldrich Syndrome protein-family verprolin-homologous protein 2 (WAVE2) and Arp2/3, play an important role in cytoskeletal reorganization and the formation of membrane protrusions that promote cancer cell migration and invasion. γ-Tocotrienol, is a natural isoform within the vitamin E family of compounds that inhibits breast cancer cell growth and progression by suppressing various signaling pathways involved in mitogenic signaling and metastatic progression. Studies were conducted to examine the effects of γ-tocotrienol on Rac1/WAVE2 signaling dependent migration and invasion in highly metastatic mouse +SA and human MDA-MB-231 mammary cancer cells. Exposure to γ-tocotrienol resulted in a dose-responsive decrease in Rac1/WAVE2 signaling as characterized by a suppression in the levels of Rac1/Cdc42, phospho-Rac1/Cdc42, WAVE2, Arp2, and Arp3 expression. Additional studies also demonstrated that similar treatment with γ-tocotrienol resulted in a significant reduction in tumor cell migration and invasion. Taken together, these findings indicate that γ-tocotrienol treatment effectively inhibits Rac1/WAVE2 signaling and reduces metastatic phenotypic expression in mammary cancer cells, suggesting that γ-tocotrienol may provide some benefit as a novel therapeutic approach in the treatment of metastatic breast cancer.

Anticancer Effects of γ-Tocotrienol Are Associated with a Suppression in Aerobic Glycolysis

Aerobic glycolysis is an established hallmark of cancer. Neoplastic cells display increased glucose consumption and a corresponding increase in lactate production compared to the normal cells. Aerobic glycolysis is regulated by the phosphatidylinositol-3-kinase (PI3K)/Akt/ mammalian target of rapamycin (mTOR) signaling pathway, as well as by oncogenic transcription factors such as c-Myc and hypoxia inducible factor 1α (HIF-1α). γ-Tocotrienol is a natural isoform within the vitamin E family of compounds that displays potent antiproliferative and apoptotic activity against a wide range of cancer cell types at treatment doses that have little or no effect on normal cell viability. Studies were conducted to determine the effects of γ-tocotrienol on aerobic glycolysis in mouse +SA and human MCF-7 breast cancer cells. Treatment with γ-tocotrienol resulted in a dose-responsive inhibition of both +SA and MCF-7 mammary tumor cell growth, and induced a relatively large reduction in glucose utilization, intracellular ATP production and extracellular lactate excretion. These effects were also associated with a large decrease in enzyme expression levels involved in regulating aerobic glycolysis, including hexokinase-II, phosphofructokinase, pyruvate kinase M2, and lactate dehydrogenase A. γ-Tocotrienol treatment was also associated with a corresponding reduction in the levels of phosphorylated (active) Akt, phosphorylated (active) mTOR, and c-Myc, but not HIF-1α or glucose transporter 1 (GLUT-1). In summary, these findings demonstrate that the antiproliferative effects of γ-tocotrienol are mediated, at least in the part, by the concurrent inhibition of Akt/mTOR signaling, c-Myc expression and aerobic glycolysis.

Synergistic anticancer effects of combined γ-tocotrienol and oridonin treatment is associated with the induction of autophagy

γ-Tocotrienol and oridonin are natural phytochemicals that display potent anticancer activity. Studies showed that combined treatment with subeffective doses of γ-tocotrienol with oridonin resulted in synergistic autophagic and apoptotic effects in malignant +SA, but not normal CL-S1 mouse mammary epithelial cells in vitro. Specifically, combined treatment with low doses of γ-tocotrienol (8 µM) and oridonin (2 µM) for 24 h resulted in synergistic inhibition of +SA mammary cancer cells viability. This combination significantly enhanced the expression of autophagy cellular markers including the conversion of LC3B-I to LC3B-II, beclin-1, Atg3, Atg7, Atg5-Atg12, LAMP-1 and cathepsin-D, and pretreatment with the autophagy inhibitors 3-methyladenine (3-MA) or bafilomycin A1 (Baf1) blocked these effects. Furthermore, blockade of γ-tocotrienol and oridonin-induced autophagy with 3-MA or Baf1 induced a modest, but significant reduction in cytotoxicity resulting from the combined treatment of these phytochemicals. The anticancer effects of combination treatment was also associated with a large suppression in Akt/mTOR mitogenic signaling and corresponding increase in the levels of apoptotic cellular marker including cleaved caspase-3 and PARP, and Bax/Bcl-2 ratio in these tumor cells. These effects were also found to be selective against cancer cells, since similar combined treatment with γ-tocotrienol and oridonin did not induce autophagy or reduce viability of normal mouse CL-S1 mammary epithelial cells. These findings indicate that combined γ-tocotrienol and oridonin-induced autophagy plays a role in mediating the synergistic anticancer effects of these phytochemicals.

δ-Tocotrienol oxazine derivative antagonizes mammary tumor cell compensatory response to CoCl2-induced hypoxia

In response to low oxygen supply, cancer cells elevate production of HIF-1α, a hypoxia-inducible transcription factor that subsequently acts to stimulate blood vessel formation and promote survival. Studies were conducted to determine the role of δ-tocotrienol and a semisynthetic δ-tocotrienol oxazine derivative, compound 44, on +SA mammary tumor cell hypoxic response. Treatment with 150 µM CoCl₂ induced a hypoxic response in +SA mammary tumor cells as evidenced by a large increase in HIF-1α levels, and combined treatment with compound 44 attenuated this response. CoCl₂-induced hypoxia was also associated with a large increase in Akt/mTOR signaling, activation of downstream targets p70S6K and eIF-4E1, and a significant increase in VEGF production, and combined treatment with compound 44 blocked this response. Additional in vivo studies showed that intralesional treatment with compound 44 in BALB/c mice bearing +SA mammary tumors significantly decreased the levels of HIF-1α, and this effect was associated with a corresponding decrease in Akt/mTOR signaling and activation of downstream targets p70S6kinase and eIF-4E1. These findings demonstrate that treatment with the δ-tocotrienol oxazine derivative, compound 44, significantly attenuates +SA mammary tumor cell compensatory responses to hypoxia and suggests that this compound may provide benefit in the treatment of rapidly growing solid breast tumors.

Synergistic Antiproliferative Effects of Combined γ -Tocotrienol and PPAR γ Antagonist Treatment Are Mediated through PPAR γ -Independent Mechanisms in Breast Cancer Cells

Previous findings showed that the anticancer effects of combined γ-tocotrienol and peroxisome proliferator activated receptor γ (PPARγ) antagonist treatment caused a large reduction in PPARγ expression. However, other studies suggest that the antiproliferative effects of γ-tocotrienol and/or PPARγ antagonists are mediated, at least in part, through PPARγ-independent mechanism(s). Studies were conducted to characterize the role of PPARγ in mediating the effects of combined treatment of γ-tocotrienol with PPARγ agonists or antagonists on the growth of PPARγ negative +SA mammary cells and PPARγ-positive and PPARγ-silenced MCF-7 and MDA-MB-231 breast cancer cells. Combined treatment of γ-tocotrienol with PPARγ antagonist decreased, while combined treatment of γ-tocotrienol with PPARγ agonist increased, growth of all cancer cells. However, treatment with high doses of 15d-PGJ₂, an endogenous natural ligand for PPARγ, had no effect on cancer cell growth. Western blot and qRT-PCR studies showed that the growth inhibitory effects of combined γ-tocotrienol and PPARγ antagonist treatment decreased cyclooxygenase (COX-2), prostaglandin synthase (PGDS), and prostaglandin D₂ (PGD₂) synthesis. In conclusion, the anticancer effects of combined γ-tocotrienol and PPARγ antagonists treatment in PPARγ negative/silenced breast cancer cells are mediated through PPARγ-independent mechanisms that are associated with a downregulation in COX-2, PGDS, and PGD₂ synthesis.

Combined γ-tocotrienol and Met inhibitor treatment suppresses mammary cancer cell proliferation, epithelial-to-mesenchymal transition and migration

OBJECTIVES

Dysregulation of Met signalling is associated with malignant transformation. Combined treatment has been shown to reduce Met activation and mammary tumour cell proliferation. Experiments here, were conducted to determine mechanisms involved in mediating anti-cancer effects of combined γ-tocotrienol and SU11274 (Met inhibitor) treatment in various mammary cancer cell lines.

MATERIALS AND METHODS

Treatment effects on mouse (+SA) and human (MCF-7, and MDA-MB-231) mammary cancer cell lines, and normal mouse (CL-S1) and human (MCF10A) mammary epithelial cell lines were compared. Cell proliferation and survival were determined by MTT assay and Ki-67 staining; protein expression was determined by western blot analysis. Immunofluorescence staining was also used to characterize expression and localization of multiple epithelial and mesenchymal markers. Cell migration was determined using a wound-healing assay.

RESULTS

Combined treatment with γ-tocotrienol and SU11274 resulted in synergistic inhibition of +SA, MCF-7, and MDA-MB-231, but not CL-S1 or MCF10A cell growth that was associated with reduction in Akt STAT1/5 and NFκB activation and corresponding blockade in epithelial-to-mesenchymal transition, as indicated by increased expression of E-cadherin, β-catenin, and cytokeratins 8/18 (epithelial markers) and corresponding reduction in vimentin (mesenchymal marker) and reduction in cancer cell motility.

CONCLUSIONS

Suggest that combined γ-tocotrienol and Met inhibitor treatment may provide benefit in treatment of breast cancers characterized by aberrant Met activity.

γ-Tocotrienol inhibits HGF-dependent mitogenesis and Met activation in highly malignant mammary tumour cells

OBJECTIVES

  Aberrant Met signalling is associated with aggressive cancer cell phenotypes. γ-tocotrienol displays potent anti-cancer activity that is associated with suppression of HER/ErbB receptor signalling. Experiments were conducted to investigate the effects of γ-tocotrienol treatment on HGF-dependent +SA mammary tumour cell proliferation, upon Met activation.

MATERIALS AND METHODS

  The +SA cells were maintained in serum-free defined media containing 10 ng/ml HGF as the mitogen. Cell viability was determined using the MTT assay, western blot analysis was used to measure protein expression, and Met expression and activation were determined using immunofluorescent staining.

RESULTS AND CONCLUSIONS

  Treatment with γ-tocotrienol or Met inhibitor, SU11274, significantly inhibited HGF-dependent +SA cell replication in a dose-responsive manner. Treatment with 4 μmγ-tocotrienol reduced both total Met levels and HGF-induced Met autophosphorylation. In contrast, similar treatment with 5.5 μm SU11274 inhibited HGF-induced Met autophosphorylation, but had no effect on total Met levels. Combined treatment with subeffective doses of γ-tocotrienol (2 μm) and SU11274 (3 μm) resulted in significant inhibition of +SA cell expansion compared to treatment with individual agents alone. These findings show, for the first time, the inhibitory effects of γ-tocotrienol on Met expression and activation, and strongly suggest that γ-tocotrienol treatment may provide significant health benefits in prevention and/or treatment of breast cancer, in women with deregulated HGF/Met signalling.

Tension, free space, and cell damage in a microfluidic wound healing assay

We use a novel, microfluidics-based technique to deconstruct the classical wound healing scratch assay, decoupling the contribution of free space and cell damage on the migratory dynamics of an epithelial sheet. This method utilizes multiple laminar flows to selectively cleave cells enzymatically, and allows us to present a 'damage free' denudation. We therefore isolate the influence of free space on the onset of sheet migration. First, we observe denudation directly to measure the retraction in the cell sheet that occurs after cell-cell contact is broken, providing direct and quantitative evidence of strong tension within the sheet. We further probe the mechanical integrity of the sheet without denudation, instead using laminar flows to selectively inactivate actomyosin contractility. In both cases, retraction is observed over many cell diameters. We then extend this method and complement the enzymatic denudation with analogies to wounding, including gradients in signals associated with cell damage, such as reactive oxygen species, suspected to play a role in the induction of movement after wounding. These chemical factors are evaluated in combination with the enzymatic cleavage of cells, and are assessed for their influence on the collective migration of a non-abrasively denuded epithelial sheet. We conclude that free space alone is sufficient to induce movement, but this movement is predominantly limited to the leading edge, leaving cells further from the edge less able to move towards the wound. Surprisingly, when coupled with a gradient in ROS to simulate the chemical effects of abrasion however, motility was not restored, but further inhibited.

Optimization of the tetrazolium dye (MTT) colorimetric assay for cellular growth and viability

The MTT colorimetric assay is an established method of determining viable cell number in proliferation and cytotoxicity studies. This assay is based on the cleavage of the yellow tetrazolium salt, MTT, to form a soluble blue formazan product by mitochondrial enzymes, and the amount of formazan produced is directly proportional to the number of living, not dead cells, present during MTT exposure. Since the MTT assay is rapid, convenient, and economical, it has become a very popular technique for quantification of viable cells in culture. However, various parameters have been identified that can affect cellular metabolism and other factors, which significantly modify MTT-specific activity and can result in calculated false high or false low cell counts. Therefore, it is essential to establish assay parameters with the proper controls for each cell line and/or drug treatment in order to optimize assay conditions and minimize confounding effects. These parameters should include determining appropriate cell densities, culture medium, optimal concentrations and exposure times for MTT, fresh culture medium at the time of assay to avoid nutrient depletion, and controlling for drug treatment effects that may influence cellular metabolism. By controlling these important parameters, the MTT colorimetric assay provides accurate and reliable quantification of viable cell number.

Mechanisms Mediating the Synergistic Anticancer Effects of Combined γ-Tocotrienol and Celecoxib Treatment

AIM: To characterize the intracellular signaling mechanisms mediating the synergistic anticancer effects of combined γ-tocotrienol and celecoxib treatment in neoplastic +SA mouse mammary epithelial cells in vitro. METHODS: +SA mammary tumor cells in different treatment groups were maintained in serum-free defined media containing 10ng/ml EGF as a mitogen and exposed to various doses of γ-tocotrienol and celecoxib alone or in combination. After a 96 hr culture period, cells were collected and whole cell lysates were subjected to Western blot analysis to determine treatment effects on intracellular signaling proteins associated with EGF-dependent mitogenesis and survival, and prostaglandin synthesis and responsiveness. RESULTS: Treatment with high doses of γ-tocotrienol or celecoxib alone inhibited Akt activation and downstream signaling and NFκB activation. Similar treatment with γ-tocotrienol also decreased concentration and activation of ErbB2-4 receptors, whereas celecoxib only inhibited ErbB2-4 receptor activation. In contrast, combined treatment with subeffective doses of γ-tocotrienol and celecoxib resulted in a large decrease ErbB2-4 receptor levels and activation, a decrease in PGE(2) levels, and a corresponding increase in prostaglandin EP2 and EP4 receptor levels. Combined treatment also induced an increase in the prostaglandin catabolizing enzyme, PGDH. CONCLUSION: The synergistic anticancer effects of combined low dose γ-tocotrienol and celecoxib treatment in +SA mammary tumor cells are mediated by COX-2-dependent mechanisms associated with a suppression in PGE(2) levels, as well as, COX-2-independent mechanisms associated with a reduction in ErbB2-4 receptor levels, activation, and subsequent reduction in downstream Akt and NFκB mitogenic signaling.

Enhanced antiproliferative and apoptotic response to combined treatment of gamma-tocotrienol with erlotinib or gefitinib in mammary tumor cells

Background

Aberrant ErbB receptor signaling is associated with various types of malignancies. γ-Tocotrienol is a member of the vitamin E family of compounds that displays potent anticancer activity that is associated with suppression in ErbB receptor phosphorylation and mitogenic signaling. Erlotinib and gefitinib are tyrosine kinase inhibitors that block ErbB1 receptor activation, whereas trastuzumab is a monoclonal antibody that has been designed to specifically inhibit ErbB2 receptor activation. However, the clinical effectiveness of these agents have been disappointing because of cooperation between different ErbB family members that can rescue cancer cells from agents directed against a single ErbB receptor subtype. It was hypothesized that targeting multiple ErbB receptor subtypes with combined treatment of γ-tocotrienol and ErbB receptor inhibitors would provide greater anticancer effects than monotherapy targeting only a single ErbB receptor subtype.

Methods

Highly malignant mouse +SA mammary epithelial cells were maintained in culture on serum-free defined media containing 10 ng/ml EGF as a mitogen. Cell viability wase determined by MTT assay, whereas Western blot and immunofluorescent staining was used to determine treatment effects on ErbB receptor subtype level and activation. Treatment-induced apoptosis was determined using annexin V staining and Western blot analysis of cleaved caspase-3 and PARP levels.

Results

Treatment with 3.5 μM γ-tocotrienol, 0.5 μM erlotinib or 1.0 μM gefitinib alone, significantly inhibited +SA tumor cell growth. Combined treatment with subeffective doses of erlotinib (0.25 μM) or gefitinib (0.5 μM) with subeffective doses of γ-tocotrienol (0.5-3.0 μM) significantly inhibited the growth and induced apoptosis in a dose-responsive manner. Trastuzumab treatment alone or in combination had no effect on +SA cell growth and viability. Combined treatment of γ-tocotrienol with erlotinib or gefitinib also cause a large decrease in ErbB3, ErbB4, and to a lesser extent ErbB2 receptor levels, and EGF-dependent ErbB2-4 tyrosine phosphorylation (activation), but had no effect on ErbB1 receptor levels or activation.

Conclusion

Combination treatment of γ-tocotrienol with specific ErbB receptor inhibitors is more effective in reducing mammary tumor cell growth and viability than high dose monotherapy, suggesting that targeting multiple ErbB receptors with combination therapy may significantly improve the therapeutic response in breast cancer patients.

Combined treatment of gamma-tocotrienol with statins induce mammary tumor cell cycle arrest in G1

Statins and gamma-tocotrienol (a rare isoform of vitamin E) both inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMGCoA) reductase activity and display anticancer activity. However, clinical application of statins has been limited by high dose toxicity. Previous studies showed that combined statin and gamma-tocotrienol treatment synergistically inhibits growth of highly malignant +SA mammary epithelial cells in culture. To investigate the mechanism mediating this growth inhibition, studies were conducted to determine the effect of combination low dose gamma-tocotrienol and statin treatment on +SA mammary tumor cell cycle progression. Treatment with 0.25 microM simvastatin, lovastatin, mevastatin, 10 microM pravastatin or 2.0 microM gamma-tocotrienol alone had no effect, while combined treatment of individual statins with gamma-tocotrienol significantly inhibited +SA cell proliferation during the 4-day culture period. Flow cytometric analysis demonstrated that combined treatment induced cell cycle arrest in G1. Additional studies showed that treatment with 0.25 microM simvastatin or 2 microM gamma-tocotrienol alone had no effect on the relative intracellular levels of cyclin D1, CDK2, CDK4 and CDK6, but combined treatment caused a large reduction in cyclin D1 and CDK2 levels. Combined treatments also caused a relatively large increase in p27, but had no effect on p21 and p15 levels, and resulted in a large reduction in retinoblastoma (Rb) protein phosphorylation at ser780 and ser807/811. Similar effects were observed following combined treatment of gamma-tocotrienol with low doses of lovastatin, mevastatin and pravastatin. These findings demonstrate that combination low dose statin and gamma-tocotrienol treatment induced mammary tumor cell cycle arrest at G1, resulting from an increase in p27 expression, and a corresponding decrease in cyclin D1, CDK2, and hypophosphorylation of Rb protein. These findings suggest that combined treatment of statins with gamma-tocotrienol may provide significant health benefits in the treatment of breast cancer in women, while avoiding myotoxicity associated with high dose statin monotherapy.

Effects of ultra-wideband electromagnetic pulses on pre-neoplastic mammary epithelial cell proliferation

Electromagnetic ultra-wideband pulses (UWB) or nanopulses, are generated by a wide range of electronic devices used in communications and radar technology. However, the specific effects of nanopulse exposure on cell growth and function have not been extensively investigated. Here, studies have been conducted to determine the effects of prolonged exposure to non-ionizing, low to moderate intensity nanopulses on the growth of pre-neoplastic CL-S1 mammary epithelial cells in vitro. Cells were grown in culture and maintained in serum-free defined medium containing 10 ng/ml EGF and 10 microg/ml insulin as comitogens. Studies showed that 0.25-3.0 h exposure to nanopulses of 18 kV/m field intensity, 1 kHz repetition rate and 10 ns pulse width had no effect on CL-S1 cell growth or viability during the subsequent 72-h culture period. However, exposure to similar nanopulses for prolonged periods of time (4-6 h) resulted in a significant increase in cell proliferation, as compared to untreated controls. Additional studies showed that nanopulse exposure enhanced CL-S1 cell growth when cells were maintained in media containing only EGF, but had no effect on cells maintained in defined media that were mitogen-free or containing only insulin. Studies also showed that the growth-promoting effects of nanopulse exposure were associated with a relatively large increase in intracellular levels of phospho-MEK1 (active) and phospho-ERK1/2 (active) in these cells. These findings demonstrate that prolonged exposure to moderate levels of UWB enhanced EGF-dependent mitogenesis, and that this growth-promoting effect appears to be mediated by enhanced activation of the mitogen-activated protein kinase (MAPK) signalling pathway in pre-neoplastic CL-S1 mammary epithelial cells.

Tocotrienol-induced caspase-8 activation is unrelated to death receptor apoptotic signaling in neoplastic mammary epithelial cells

Tocotrienols, a subclass in the vitamin E family of compounds, have been shown to induce apoptosis by activating caspase-8 and caspase-3 in neoplastic mammary epithelial cells. Since caspase-8 activation is associated with death receptor apoptotic signaling, studies were conducted to determine the exact death receptor/ligand involved in tocotrienol-induced apoptosis. Highly malignant +SA mouse mammary epithelial cells were grown in culture and maintained in serum-free media. Treatment with 20 microM gamma-tocotrienol decreased+SA cell viability by inducing apoptosis, as determined by positive terminal dUTP nick end labeling (TUNEL) immunocytochemical staining. Western blot analysis showed that gamma-tocotrienol treatment increased the levels of cleaved (active) caspase-8 and caspase-3. Combined treatment with caspase inhibitors completely blocked tocotrienol-induced apoptosis. Additional studies showed that treatment with 100 ng/ml tumor necrosis factor-alpha (TNF-alpha), 100 ng/ml FasL, 100 ng/ml TNF-related apoptosis-inducing ligand (TRAIL), or 1 microg/ml apoptosis-inducing Fas antibody failed to induce death in +SA cells, indicating that this mammary tumor cell line is resistant to death receptor-induced apoptosis. Furthermore, treatment with 20 microM gamma-tocotrienol had no effect on total, membrane, or cytosolic levels of Fas, Fas ligand (FasL), or Fas-associated via death domain (FADD) and did not induce translocation of Fas, FasL, or FADD from the cytosolic to the membrane fraction, providing additional evidence that tocotrienol-induced caspase-8 activation is not associated with death receptor apoptotic signaling. Other studies showed that treatment with 20 microM gamma-tocotrienol induced a large decrease in the relative intracellular levels of phospho-phosphatidylinositol 3-kinase (PI3K)-dependent kinase 1 (phospho-PDK-1 active), phospho-Akt (active), and phospho-glycogen synthase kinase3, as well as decreasing intracellular levels of FLICE-inhibitory protein (FLIP), an antiapoptotic protein that inhibits caspase-8 activation, in these cells. Since stimulation of the PI3K/PDK/Akt mitogenic pathway is associated with increased FLIP expression, enhanced cellular proliferation, and survival, these results indicate that tocotrienol-induced caspase-8 activation and apoptosis in malignant +SA mammary epithelial cells is associated with a suppression in PI3K/PDK-1/Akt mitogenic signaling and subsequent reduction in intracellular FLIP levels.

Role of GTP-binding proteins in reversing the antiproliferative effects of tocotrienols in preneoplastic mammary epithelial cells

Tocotrienols are a subclass of vitamin E compounds that display potent anticancer activity. Determining the anticancer mechanism of action of tocotrienols will provide essential information necessary for understanding the potential health benefits of these compounds in reducing the risk of breast cancer in women. Epidermal growth factor (EGF) is a potent mitogen for normal and neoplastic mammary epithelial cells. Initial events in EGF-receptor (EGF-R) mitogenic-signalling are G-protein activation, stimulation of adenylyl cyclase and cyclic AMP (cAMP) production. Studies were conducted to determine if the antiproliferative effects of tocotrienols are associated with reduced EGF-induced G-protein and cAMP-dependent mitogenic signalling. Preneoplastic CL-S1 mouse mammary epithelial cells were grown in culture and maintained on serum-free media containing 0-25 micro mol/L tocotrienol-rich fraction of palm oil and/or different doses of pharmacological agents that alter intracellular cAMP levels. Tocotrienol-induced effects on EGF-receptor levels of tyrosine kinase activity, as well as EGF-dependent mitogen-activated pathway kinase (MAPK) and Akt activation, were determined by western blot analysis. Results demonstrate that the antiproliferative effects of tocotrienols in preneoplastic mammary epithelial cells do not reflect a reduction in EGF-receptor mitogenic responsiveness, but rather, result from an inhibition in early post-receptor events involved in cAMP production upstream from EGF-dependent MAPK and phosphoinositide 3-kinase/Akt mitogenic signalling. In summary, these data further characterise the mechanism of action of tocotrienols in suppressing preneoplastic mammary epithelial cell proliferation, and advance the current understanding of the potential health benefits of these compounds in reducing the risk of breast cancer in women.

Antiproliferative and apoptotic effects of tocopherols and tocotrienols on preneoplastic and neoplastic mouse mammary epithelial cells

Studies were conducted to determine the comparative effects of tocopherols and tocotrienols on preneoplastic (CL-S1), neoplastic (-SA), and highly malignant (+SA) mouse mammary epithelial cell growth and viability in vitro. Over a 5-day culture period, treatment with 0-120 microM alpha- and gamma-tocopherol had no effect on cell proliferation, whereas growth was inhibited 50% (IC50) as compared with controls by treatment with the following: 13, 7, and 6 microM tocotrienol-rich-fraction of palm oil (TRF); 55, 47, and 23 microM delta-tocopherol; 12, 7, and 5 microM alpha-tocotrienol; 8, 5, and 4 microM gamma-tocotrienol; or 7, 4, and 3 microM delta-tocotrienol in CL-S1, -SA and +SA cells, respectively. Acute 24-hr exposure to 0-250 microM alpha- or gamma-tocopherol (CL-S1, -SA, and +SA) or 0-250 microM delta-tocopherol (CL-S1) had no effect on cell viability, whereas cell viability was reduced 50% (LD50) as compared with controls by treatment with 166 or 125 microM delta-tocopherol in -SA and +SA cells, respectively. Additional LD50 doses were determined as the following: 50, 43, and 38 microM TRF; 27, 28, and 23 microM alpha-tocotrienol; 19, 17, and 14 microM gamma-tocotrienol; or 16, 15, or 12 microM delta-tocotrienol in CL-S1, -SA, and +SA cells, respectively. Treatment-induced cell death resulted from activation of apoptosis, as indicated by DNA fragmentation. Results also showed that CL-S1, -SA, and +SA cells preferentially accumulate tocotrienols as compared with tocopherols, and this may partially explain why tocotrienols display greater biopotency than tocopherols. These data also showed that highly malignant +SA cells were the most sensitive, whereas the preneoplastic CL-S1 cells were the least sensitive to the antiproliferative and apoptotic effects of tocotrienols, and suggest that tocotrienols may have potential health benefits in preventing and/or reducing the risk of breast cancer in women.

Decreased Egr-1 expression in human, mouse and rat mammary cells and tissues correlates with tumor formation

We have examined several types of tumor cell lines and shown that they invariably expressed little or no Egr-1, in contrast to their normal counterparts. We have previously shown that the expression of exogenous Egr-1 in human breast and other tumor cells markedly reduces transformed growth and tumorigenicity. We therefore hypothesized that the loss of Egr-1 expression plays a role in transformation. All human and mouse breast cancer cell lines and tumors examined had reduced Egr-1 expression compared with their normal counterparts. Reduced Egr-1 expression was also observed in 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumors, and this level increased to normal levels in tumors that regressed after tamoxifen treatment. We concluded, therefore, that loss of Egr-1 expression may play a role in the deregulation of normal growth in the tumorigenic process and that Egr-1 acts as a tumor suppressor gene.

HH2A, an immortalized bovine mammary epithelial cell line, expresses the gene encoding mammary derived growth inhibitor (MDGI)

We have established and partially characterized a spontaneously immortalized bovine mammary epithelial cell line, designated HH2a. The cells express the gene encoding for mammary derived growth inhibitor (MDGI) when grown on released collagen gels in the presence of lactogenic hormones. This is the first report of a cell line that expresses MDGI. Immunohistochemical studies showed that HH2a cells contain keratin intermediate filaments and desmosomes. When plated on confluent monolayer of live fibroblasts, HH2a cells extensively contacted with fibroblasts. When embedded in the collagen gels, they rearranged themselves to produce three-dimensional duct-like outgrowths extending into the matrix. The HH2a cell line should be useful in investigations of the roles of cell-cell and cell-extracellular interactions in regulation of breast epithelial cell proliferation, and of the hormonal regulation of MDGI gene expression.

Microprocedure for in situ nick translation of chromosomes

We have modified the procedure of in situ nick translation to shorten the autoradiographic exposure time from 1 month to 3 days and reduce the volume of nick translation solution by a factor of at least 10. The modified procedure can be carried out on individually chosen chromosome spreads. The procedure was used on chromosome spreads of three related lines of mouse mammary epithelium (+SA, -SA, CL-S1) with different degrees of tumorigenicity. We found that the autoradiographic silver grains that are observed following in situ nick translation were often placed at the apparent junction site of chromosome translocations or at the breakpoint of chromosomal pieces. We found also that silver grains were located above double minute chromosomes, which suggests that there are active genes in double minutes.

Correlation of hyaluronic acid accumulation and the growth of preneoplastic mammary cells in collagen: a longitudinal study

Hyaluronic acid accumulation is characteristic of mammary tumor cells, and the amount that accumulates seems to correlate with the degree of malignancy of the producing cells. We have tested directly the relationship between hyaluronic acid accumulation and the replication rate of preneoplastic mammary cells in culture. We used nontumorigenic but immortal CL-S1 mouse mammary cells that were derived from a hyperplastic alveolar nodule. Using a collagen gel culture system, we found clear differences in the growth properties of cells before and after Passages 68 to 70. Late passage cells replicated earlier and faster than early passage cells in collagen and on plastic. The rate of cycling resembled that of tumorigenic mouse mammary cells during the first week of culture. Cells seeded at low densities cycled faster than those seeded at high densities during the second week in culture. Exogenous hyaluronic acid, at 10 to 1000 micrograms/ml, neither enhanced nor inhibited CL-S1 cell growth significantly in collagen, regardless of passage. However, by the third day in collagen, late passage cells produced 7 times more total glycosaminoglycans and 12 times more hyaluronic acid per cell than did early passage cells. Late passage cells also deposited 12 times more labeled hyaluronic acid in the matrix than did early passage cells, on a per-cell basis. After a decline in the deposition of hyaluronic acid in the extracellular matrix, growth ceased. The late passage cells did not grow in soft agar, indicating that they had not become neoplastic spontaneously during passage. However, their accelerated growth rate, coupled with the synthesis and secretion of large amounts of hyaluronic acid into the extracellular matrix, may characterize a distinct step in tumor progression in preneoplastic CL-S1 cells.

Growth factor interactions between mouse mammary cell lines cocultured in collagen gels

Three related mouse mammary cell lines were cultured in collagen gels and assayed for growth factor responsiveness and interaction via soluble factors. The CL-S1 cell line is nontumorigenic and grows poorly in collagen gel culture. The +SA and -SA cell lines exhibit different degrees of malignant behavior in vivo and have different growth properties in vitro. In collagen gel culture, +SA growth was stimulated by serum but not by epidermal growth factor (EGF), whereas both serum and EGF were required for optimal growth of -SA cells of early passage number as well as CL-S1 cells. -SA cells of later passage repeatedly exhibited a change so as to no longer require serum while retaining EGF responsiveness. [125I]EGF binding analyses indicated that CL-S1 cells bound EGF with less affinity than did -SA cells whereas +SA cells bound almost no ligand. When cell lines were maintained in separate collagen gels but shared the same culture medium, growth of +SA or -SA cells was slightly enhanced in the presence of CL-S1 cells and -SA cell growth was enhanced by the presence of +SA cells. Using the normal rat kidney fibroblast line NRK (clone 49F) as an indicator, serum-containing conditioned media from each cell line and from each pair of cell lines cultured in collagen gels were tested for transforming growth factor (TGF) activity. Both the -SA and CL-S1 lines tested positive for TGF-alpha production and possibly released a TGF-beta activity. These results suggest mechanisms by which cell populations in and around tumors can modify one another's growth characteristics.

Growth of epithelium from a preneoplastic mammary outgrowth in response to mammary adipose tissue

We investigated the effects of conditioned media derived from mouse mammary fat pads on the proliferation of CL-S1 cells, an epithelial cell line originally isolated from a preneoplastic mammary outgrowth line. Cell proliferation in vitro in serum-free defined medium was compared to that in this medium conditioned using intact mammary fat pad pieces or isolated fat pad adipocytes. Culture medium was conditioned by incubating the conditioning material in defined culture medium for 24 h at 37 degrees C. Conditioned medium induced CL-S1 proliferation as much as 10- to 20-fold above the minimal levels of growth in control cultures after 13 d of culture. The growth-stimulatory factor(s) had an apparent molecular weight of greater than 10 kDa. This growth-stimulatory activity was both heat and trypsin stable. Because the role of adipose tissue is to store and release lipids, we next tested whether lipids are released during medium conditioning. The lipid composition of the fat pad conditioned medium was characterized using both thin layer and gas liquid chromatography. These lipid analyses indicated that the fat pad pieces released significant amounts of fatty acids and phospholipids into the medium during the conditioning period. The free fatty acid composition included both saturated and unsaturated molecules, and about 80% of the total fatty acids consisted of palmitate, stearate, oleate, and linoleate. These same fatty acids were a structural component of the majority of phospholipid found in the medium. The addition of palmitate or stearate to defined medium had no effect or was inhibitory for CL-S1 proliferation, depending on the concentration used. Defined medium supplemented with oleate, arachidonate, or linoleate induced CL-S1 proliferation, and the inhibitory effects of palmitate and stearate were overcome by addition of oleate and linoleate. These data indicate that both unsaturated and saturated fatty acids are released from intact adipose cells of the mouse mammary fat pad and that fatty acids can influence the growth of preneoplastic mouse mammary epithelium. Thus, unsaturated fatty acids, perhaps in conjunction with other substances released simultaneously, are candidate molecules for the substances that mediate the effect of adipose tissue on growth of epithelium.

New mammary epithelial and fibroblastic cell clones in coculture form structures competent to differentiate functionally

We have established and characterized a spontaneously immortalized, nontumorigenic mouse mammary cell line, designated IM-2. IM-2 cells synthesize large amounts of the milk protein beta-casein upon addition of lactogenic hormones. The induction of beta-casein occurs rapidly and does not require any exogenous extracellular matrix components. The IM-2 cell line is morphologically heterogeneous and could be separated into cell clones with epithelial and fibroblastic characteristics. In monoculture, none of the epithelial clones could be induced to synthesize caseins. Coculture of epithelial and fibroblastic clones, however, rendered the epithelial cells competent to differentiate functionally; the addition of lactogenic hormones to these cocultures resulted in the synthesis of beta-casein in amounts comparable to that seen with the original IM-2 line. Using this unique cell system, we have investigated the interrelationships between different steps in differentiation leading to hormone-induced casein production. Independent of hormones, epithelial-fibroblastic cell contacts led to the formation of characteristic structures showing the deposition of laminin. We found that the epithelial cells located in these structures also exhibited significantly increased levels of cytokeratin intermediate filament polypeptides. Double immunofluorescence revealed that the cells inducible by hormones to synthesize casein, colocalized exactly with the areas of laminin deposition and with the cells showing greatly intensified cytokeratin expression. These results suggest that hormone-independent differentiation events take place in response to intercellular epithelial-mesenchymal contacts. These events in turn bring about a state of competence for functional differentiation after lactogenic hormonal stimulation.

Epithelial mouse mammary cell line exhibiting normal morphogenesis in vivo and functional differentiation in vitro

An epithelial cell line, designated COMMA-1D, was derived from mammary tissue of BALB/c mice in the middle of pregnancy. This line, in continuous cell culture for 12 months, exhibits several characteristics distinctive of normal mammary epithelial cells, including induction of casein synthesis in vitro and normal duct morphogenesis in the cleared mammary fat pads of syngeneic mice. The cells also form domes in high density culture and are positive for keratin intermediate filaments by indirect immunofluorescence. COMMA-1D cells have a near diploid number of chromosomes and do not grow in suspension culture or produce tumors in syngeneic hosts. This cell line should prove useful for studies examining the regulation of normal cellular differentiation of mammary cells as well as transformation of epithelial cells to the preneoplastic and neoplastic phenotypes.

Transformation of mouse mammary epithelial cells by papovavirus SV40

Primary and established murine mammary epithelial cells and wild-type SV40 were employed to study the phenomenon of epithelial cell transformation. Thirteen independent transformed cell lines were derived. All contained SV40 intranuclear T antigen. Eight transformed mammary cell lines were examined ultrastructurally and all were found to exhibit pronounced epithelial cell characteristics, including desmosomes and tight junctions. Growth studies revealed that while normal mammary cells were unable to grow in low serum (2% FBS), established Cl S1 mammary cells and SV40-transformed mammary epithelial cells replicated well. Cell densities achieved by the transformants were only slightly elevated in high serum (13% FBS) over normal cell values. All the transformants formed colonies on plastic and exhibited anchorage-independent growth in methylcellulose. Five of the transformed lines were tumorigenic in syngeneic animals, in marked contrast to the lack of transplantability usually observed with SV40-transformed mouse fibroblasts. Anchorage-independent growth was not a predictor of tumorigenic potential in this system. The transformants exhibited a spectrum of responsiveness to exogenous growth factors. This study establishes that the SV40-murine mammary cell system is a valid model for analyses of the process and consequences of epithelial cell transformation, in general, and mammary cell transformation in particular.

Assessing tumor drug sensitivity by a new in vitro assay which preserves tumor heterogeneity and subpopulation interactions

We have designed an in vitro assay to assess the influence of tumor subpopulation interactions on drug response. The assay is based upon inhibition of growth of 1 mm3-pieces of tumor embedded in a collagen gel matrix. Tumor growth is quantitated by planimetry of each colony's image, formed with a split image tracing device attached to an inverted microscope. That expansion of the colonies in collagen gel represents growth through cell replication was demonstrated by releasing and counting cell nuclei. Outgrowths from pieces of tumors produced by a series of mouse mammary tumor subpopulation lines expanded in collagen gel at a rate characteristic of each cell line: the growth rate of tumor pieces was similar to that of the corresponding tumor line embedded as a cell bolus of cultured cells, indicating that growth of pieces of tumor is due to the tumor cells rather than to stromal components. When two cell lines were grown together in collagen cultures, interactions affecting growth rate were observed. Both tumor pieces and cell boluses from cultured cells of the relatively homogeneous cell lines displayed similar, characteristic sensitivities to adriamycin (ADR) in the collagen gel assay. Advantages of the collagen assay over cloning assays are (1) preservation of potential cellular interactions which may be important in assessing tumor drug sensitivity; (2) maximization of growth of all cell populations within the tumor, as compared to growth in agar; and (3) reflection of the zonal distribution of different subpopulations within tumors; and (4) simulation of the three-dimensional growth architecture found in vivo.

Growth of cells in culture treated with the soluble component of volcanic ash from Mount St. Helens

Volcanic ash was collected immediately after the eruption of Mount St. Helens on May 18, 1980. This ash was extracted with water. The elemental composition of the extracted portion was determined by atomic absorption spectrometry. The aqueous extract was applied at high concentrations (up to 37.5 micrograms/ml) to non-confluent mixed cultures of mouse lung cells. Even after treatment for up to 10 days, cell number was typically unaffected by the ash extract. Cell viability was also unaltered, and no grossly observable changes were noted in the cells by light microscopy. We conclude that the water-soluble portion of the ash we tested does not markedly affect growth of the cells most at risk, those of the lung.

Uptake and localization of selenium-75 in mammary epithelial cell lines in vitro

The uptake and subcellular localization of selenium-75 was examined in 3 established mammary cell lines in vitro. Previous studies had demonstrated that cell line YN-4 exhibited a biphasic growth response to selenium, whereas cell lines CL-S1 and WAZ-2t exhibited only an inhibition of growth. All 3 cell lines incorporated selenium-75 readily over a 48-h incubation period and the concentration of selenium-dependent glutathione peroxidase was correlated with the level of selenium-75 uptake. However, neither of these 2 parameters could be related to the unique biphasic growth response exhibited by cell line YN-4. The intracellular localization of selenium-75 was similar in lines CL-S1 and YN-4 with the label incorporated primarily in the cytosol and secondarily in the mitochondria. Although the unique growth response of line YN-4 could not be attributed to the incorporation parameters examined herein, the stable incorporation of selenium-75 at high levels should make these lines useful for further studies on the subcellular localization of selenium into organelles and macromolecules.

Differential effects of selenium on the growth of mouse mammary cells in vitro

The effect of selenium was examined on the growth potential of normal, preneoplastic and neoplastic mammary cells grown in primary monolayer cell cultures and on 3 established mammary cell lines. Selenium, present as Na2SeO3 in serum-free DMEM, inhibited all mammary cell cultures at 1 x 10(-5) M. Selenium, at 5 x 10(-8) M, stimulated the growth of primary cell cultures of normal mammary cells and C4 preneoplastic cells and the established cell line YN-4, but not the growth of D2 preneoplastic cells and tumors in primary cell cultures and of established cell lines CL-S1 and WAZ-2t. The differential responses of cells from preneoplastic outgrowth lines C4 and D2 and of D2 primary tumors in vitro correlated with the sensitivity of these same cell populations to selenium-mediated inhibition of growth and tumorigenesis in vivo. The differential responses among the 3 cell lines will allow further comparative studies on the cell biological basis of selenium function.